1. Field of the Invention
This invention relates to a camera having dual focal plane photocells for participating in the control of predetermined exposure parameters during the exposure of adjacent portions of the same film unit.
2. Description of the Prior Art
It is generally accepted that one of the most advantageous places to locate a photocell so as to achieve the highest degree of accuracy is directly in front of the film plane close to the surface of the film which is subsequently exposed upon opening of the camera's shutter. However, because the photocell is situated directly in front of the film prior to exposure thereof, it is essential to move the photocell away from its location in front of the film out of the path of light travelling toward the film plane when the shutter is opened to make the actual exposure. Accordingly, mechanisms such as that shown in U.S. Pat. No. 3,690,241 have been described which will operate in a manner to bring about the required movement of a photocell to and from its operative position situated directly in front of the film plane.
One of the problems with a mechanism of the type described in the aforementioned patent is that there is no photocell which is measuring the intensity of the light at the film plane during the exposure of the film. Should the intensity of the light being reflected from the scene being photographed change during the interval that the shutter is open the resulting exposure will be adversely affected. For example, during the exposure interval, a cloud may suddenly partially obscure the sun or the crest of an ocean wave may collapse thereby altering the intensity of the light to which the film is being exposed.